1. Field of the Invention
The present invention relates to a drive unit for driving a vehicle mirror or the like in four directions, and more particularly, to a drive unit which is capable of appropriately operating the mirror when plural directions are simultaneously selected by an operation member.
2. Description of the Related Art
A drive unit capable of driving a vehicle mirror in four directions remotely at a driver's seat is used for adjusting an angle of the mirror surface both vertically and laterally. The drive unit includes an operation member which can be operated in four directions, that is, up, down, left and right, a switch section which is turned ON and OFF in response to the operation of the operation member, a pair of motors connected to the switch section, and a power wire and a grounding wire both connected to the switch section.
FIG. 20 is a circuit diagram of a drive unit of the related art. Referring to the drawing, the drive unit includes a pair of motors 50, 51, a switch section 52 formed of plural switches, a power wire 53 and a grounding wire 54. The motor 50 that is one of the pair of motors is used for vertical driving operations and the motor 51 that is the other thereof is used for lateral driving operations.
The switch section 52 includes a common terminal 52a connected to a terminal at one end of the motor 50 and a terminal at one end of the motor 51, a first terminal 52b connected to a terminal at the other end of the motor 50, and a second terminal 52c connected to a terminal at the other end of the 51. The motor 50 is connected to the common terminal 52a and the first terminal 52b, and rotated forward or reversely upon operation of the switch section 52. The other motor 51 is connected to the common terminal 52a and the second terminal 52c, and rotated forward or reversely upon operation of the switch section 52.
Each of the switches constituting the switch section 52 is formed of a two-contact switch so as to be switchable between ON and OFF. FIG. 21 illustrates a layout of the switches. Referring to the drawing, switch groups each including two switches are arranged at the positions corresponding to up, down, left and right directions, respectively, to form the switch section 52.
Operation states of the drive unit with the aforementioned structure are illustrated in a table shown in FIG. 22. The table shows states of the respective terminals of the switch section 52, and operation directions of the motors 50 and 51. The table further represents the case where a tilting operation is performed in one of four directions by the operation member and two switches in the selected direction are operated simultaneously, and the case where the operation member is tilted with a large force in the direction between two adjacent directions, and four switches in the two adjacent directions are operated simultaneously. Referring to the table, the symbol “U” denotes the up direction, “D” denotes the down direction, “R” denotes the right direction, and “L” denotes the left direction relative to the direction of the operated switch and the motor operation direction. The symbols “H”, “L” and “Z” in a section of “terminal output” in the table denote a state connected to the power wire 53, a state connected to the grounding wire 54, and an open state, respectively. Those symbols are employed in the following description.
Referring to FIG. 22, when the operation in one direction selected from the four directions is performed by the operation member, two switches corresponding to the tilting direction are activated to enable the motors 50 and 51 to perform predetermined operations. Meanwhile, in the case where the operation member is tilted in the direction between the down and right directions, that is, the direction DR, the switches D1, D2, R1 and R2 are turned ON to connect the common terminal 52a to the power wire, and the first terminal 52b and the second terminal 52c to the grounding wire so as to activate the two motors 50 and 51 simultaneously. In the case where the tilting operation is performed in the direction between the up and left directions, that is, the direction UL, the switches U1, U2, L1 and L2 are turned ON to connect the common terminal 52a to the grounding wire, and the first terminal 52b and the second terminal 52c to the power wire so as to activate the two motors 50 and 51 simultaneously as well. In the case where the tilting operation is performed in the direction between the up and the right directions, that is, the direction UR, the switches U1, U2, R1 and R2 are turned ON simultaneously. As the switches U2 and R1 are simultaneously turned ON, the short circuit may occur. The tilting operation in the direction between the down and the left directions, that is, the direction DL turns the switches L1, L2, D1 and D2 ON simultaneously. As the switches L1 and D2 are simultaneously turned ON, the short circuit may occur likewise the case as described above.
In addition to the two-contact switch constituting the switch section 52, a three-contact switch having a common contact and two switching contacts has been known and used to constitute the switch section. The use of the three-contact switch prevents the short circuit caused by simultaneously operating the operation member in plural directions. The above-structured drive unit is disclosed in Japanese Unexamined Patent Application Publication No. 64-36538, for example.
The disclosed drive unit is structured to allow three switches to be operated in four ways in response to the operation of the operation member. However, the specific structure of the switch and the process for the switching operation are not disclosed. The behavior of the drive unit operated in a predetermined direction is unstable, which may fail to bring the operation into a stable state.